GPS Navigation

GPS Navigation is becoming an essential tool in our daily routine. It helps us find our Point Of Interest (POI) and guides us to our destination without asking for directions. In addition to turn by turn directions, navigation devices offer many other features that include traffic, closest emergency services (Police stations, Hospitals, Fuel stations), gas prices, 3D Street View, ect.

Few short years ago navigation was a luxury item available only in luxury cars. It is now available in medium level vehicle and in some economy models.

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How does GPS work?

When people talk about "a GPS," they usually mean a GPS receiver. The Global Positioning System (GPS) is actually a constellation of 27 Earth-orbiting satellites (24 in operation and three extras in case one fails). The U.S. military developed and implemented this satellite network as a military navigation system, but soon opened it up to everybody else

Each of these 3,000- to 4,000-pound solar-powered satellites circles the globe at about 12,000 miles (19,300 km), making two complete rotations every day. The orbits are arranged so that at anytime, anywhere on Earth, there are at least four satellites "visible" in the sky.

A GPS receiver's job is to locate four or more of these satellites, figure out the distanc­e to each, and use this information to deduce its own location. This operation is based on a simple mathematical principle called trilateration. Trilateration is the method of locating a receiver by using measured distances from three satellites to that receiver.

GPS receivers passively receive satellite signals; they do not transmit. They require an unobstructed view of the sky, so they are used only outdoors and their performance is sometimes affected within forested areas or near tall buildings. GPS operations depend on a very accurate time reference, which is provided by atomic clocks at the U.S. Naval Observatory. Each GPS satellite has atomic clocks on board.

Each GPS satellite transmits data that indicates its location and the current time. All GPS satellites synchronize operations so that these repeating signals are transmitted at the same instant. The distance to the GPS satellites can be determined by estimating the amount of time it takes for their signals to reach the receiver. When the receiver estimates the distance to at least four GPS satellites, it can calculate its position in three dimensions.